Such devices are previously known from the documents WO 96/37922 (Allgon AB) and WO02/35651 A1 (Allgon AB). The device known from WO 96/37922 comprises a feed line structure integrated with a stationary array of antenna elements so as to enable adjustment of the direction of the beam radiated from the array. The feed line structure includes a feed conductor line pattern disposed on a fixed dielectric carrier plate at a distance from and in parallel to a fixed ground plate. The feed line structure is disposed on the carrier plate surface facing away from the ground plate. A movable dielectric plate is located between the carrier plate and the ground plate. The feed line pattern is elongated in the same direction as the movement direction of the dielectric plate. The propagation velocity of the signal components is reduced by the presence of the dielectric plate between the respective feed line and the ground plate. Accordingly, by displacing the dielectric plate in the longitudinal direction, the phase difference between the various signal components may be controlled. A problem with the device described in WO 96/37922 is that the influence on the signal phase, and thus the beam angle, is relatively low.
WO02/35651 A1 relates to a device for adjusting the beam direction of an antenna comprising a plurality of antenna elements coupled to a common signal source by means of a feed line structure consisting of punched metal lines. The feed line structure is extended in a main direction and positioned in parallel to one or two ground planes, wherein a movable dielectric element is located between the feed line structure and each ground plane in order to achieve a controlled phase shift to thereby adjust the beam direction of the antenna. The dielectric element consists of different portions having different effective dielectric values. A problem with the device described in WO02/35651 is mechanical tolerances.
A problem with both of the above described solutions is that it is difficult to ensure that an intended beam tilt angle actually results in a set beam tilt angle corresponding to the intended beam tilt angle.